1. Field of the Invention
The present invention relates to an image display apparatus and a control method thereof.
2. Description of the Related Art
As a flat panel display (FPD), a liquid crystal display (LCD), plasma display (PDP), organic EL display (OLED) and field emission display (FED) among others are known.
FED having a passive matrix structure in particular has characteristics of low cost and high-speed response, because it has a simple panel structure where a field emitting device is positioned at an intersection of a row wiring and a column wiring.
FIG. 1 is a diagram depicting a basic configuration example of a general matrix driving type image display apparatus (e.g. FED). A plurality of column wirings 104 and a plurality of row wirings 105 are formed on the rear substrate 106, and a pixel (display device) is formed on each intersection of a column wiring 104 and a row wiring 105. A display apparatus module is constructed by the column wirings 104 connected to a column wiring driving circuit 102 and the row wirings 105 connected to a row wiring driving circuit 103.
The image display apparatus in FIG. 1 also has a control circuit 101 to which digital image signals are input. The row wiring driving circuit 103 is a circuit that applies a scanning signal (selection voltage) to a driving target row wirings 105 and an unselection voltage to the other row wirings 105. Row wirings 105 are sequentially driven (scanned) one line at a time from the top, for example. The column wiring driving circuit 102 generates a driving waveform (modulation signal) of each column based on an image signal (brightness signal) of a driving row, and applies the driving waveform to each column wiring 104. Thereby a brightness of the display device (electron emitting amount of the electron emitting device) is modulated, and a desired image can be output.
However because of the wiring resistance of the column wirings 104 and the electrostatic capacitance generated at the intersections of the column wirings 104 and row wirings 105, voltage of the modulation signals drops, and the waveform is rounded by the RC time constant. Due to this, as shown in FIG. 12 the form of a modulation signal to be applied to a display device disposed close to the column wiring driving circuit 102 (driving end side) and that to be applied to a display device disposed distant from the column wiring driving circuit 102 (open end side) become different. As a result, the open end side becomes darker than the driving end side. In other words, brightness unevenness (display failure) is generated in the column direction.
Furthermore, a column wiring 104 becomes longer and thinner as the size of the image display apparatus becomes larger, and the resolution thereof becomes higher. Since this increases the resistance of the column wirings 104, brightness unevenness increases even more than the above mentioned case.
The proposed technologies for solving this problem are, for example, a technology for correcting image signals using correction values according to the position of the display device and gradation (U.S. Pat. No. 6,097,356), and a technology for correcting the image signals according to rounding of the voltage signal due to the RC time constant (Japanese Patent Application Laid-Open No. H6-258614). If these technologies are used, the above mentioned display failure can be controlled (corrected).